On Thu, 18 Oct 2007, Kay Sievers wrote:
> On Thu, 2007-10-18 at 15:23 -0400, Alan Stern wrote:
> > This patch (as1004) fixes a refcounting bug in the development version
> > of the block-device core.
> >
> > Signed-off-by: Alan Stern <[EMAIL PROTECTED]>
> >
> > ---
> >
> > Kay, you have got to start testing your patches better!
>
> That leaves references around for SCSI target devices. There must be a
> bug somewhere else, if the patch isn't correct.
>
> > Finding and
> > fixing refcount errors is _not_ one of my favorite ways to pass the
> > time. For example, you could see what happens when you insert and
> > unplug a USB flash disk a few times.
>
> What do you see with the original version?
Note that a USB drive is treated as a SCSI device.
With the original code, I see the following sequence of events when
add_disk() is first called. Values in parentheses are
atomic_read(disk->dev.kobj.kref.refcount) after each stage runs:
Entry to add_disk (1)
Call to register_disk
device_add (3)
CONFIG_SYSFS_DEPRECATED is not set
Call disk_sysfs_add_subdirs
add disk->holder_dir (4)
add disk->slave_dir (5)
Return to register_disk
get_capacity (5)
bdget_disk (5)
blkdev_get (partitions) (8)
blkdev_put (7)
Return to add_disk
blk_register_queue (9)
You can see how many references each stage takes. Now here's the
equivalent list for del_gendisk():
Entry to del_gendisk (9)
invalidate_ and delete_partition loop (7)
invalidate_partition 0 (7)
Call unlink_gendisk
blk_unregister_queue (5)
Return to del_gendisk
unregister disk->holder_dir (4)
unregister disk->slave_dir (3)
CONFIG_SYSFS_DEPRECATED is not set
device_del (1)
put_device (0) -- oops!
Matching things up we have:
device_add/device_del 2 refs
reg/unreg subdirs 2 refs
subpartitions 2 refs
reg/unreg block queue 2 refs
This accounts for everything in del_gendisk except the final
put_device. Evidently it doesn't belong there. There's no matching
get_device in add_disk or register_disk.
Alan Stern
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